1. Field of the Invention:
This invention relates to motion conversion mechanisms. More specifically, this invention relates to motion conversion mechanisms driven by a rotating member.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art:
Scanning imaging systems are currently utilized in a variety of applications. For example, scanning imaging systems have been used in planetary mapping and in medical imaging. Such scanning systems typically require a scanning member to survey a field of view in a bidirectional or unidirectional manner. A mirror or imaging device attached to the scanning member may then be utilized to sequentially focus on individual regions within a scene. In this manner electromagnetic energy collected from each region within the scene is used to construct an image.
Scanning members may be driven by a number of mechanisms. For example, when a bidirectional harmonic scan is desired a spring mechanism may be employed to drive the scanning member. A harmonic scan is one in which the displacement versus time plot for the scanning member (relative to a fixed reference) assumes a sinusoidal shape. The scanning member is driven when the spring mechanism is displaced from a rest position and thereby induced to oscillate.
If nonlinearities are desired in a harmonic scan, resistive elements may be included within the spring mechanism. These resistive elements oppose oscillation of the spring mechanism in a predetermined manner and thereby enable perturbation of the harmonic scan. However, spring mechanisms are typically limited to applications requiring a scanning motion having a fundamentally harmonic (sinusoidal) component. Moreover, the maximum scan velocity afforded by harmonic scan mechanisms is inadequate for certain applications. Further, spring elements within such spring mechanisms may become fatigued and break after prolonged usage.
When a nonlinear, nonharmonic scan is desired driving mechanisms often termed "Geneva" mechanisms may be utilized. A standard Geneva mechanism includes a "driver"0 and a "follower". The driver is typically disk-shaped while the periphery of the follower generally includes a plurality of U-shaped slots. In most instances the driver is kept in uniform rotation by an external motor. A pin fastened to the driver sequentially engages the slots of the follower. For continuous rotation of the driver, the follower alternately rolls with the driver and then remains stationary. In this manner a standard Geneva mechanism generates an intermittent, unidirectional scanning motion from a continuous rotary motion.
The relative sizes of the driver and follower, and the number of slots included in the follower are the parameters typically manipulated when designing a standard Geneva mechanism for a particular application. By varying these parameters and adjusting the rotational speed of the driver, Geneva mechanisms can be designed for nonharmonic unidirectional scanning applications.
However, scanning members coupled to standard Geneva mechanisms are limited to scanning angles of 90 degrees or less. This constraint typically prevents standard Geneva mechanisms from being utilized in applications requiring a wide scan angle. Further, due to the unidirectional rotation of the driver within standard Geneva mechanisms, such mechanisms are unable to provide a bidirectional (oscillatory) scan.
Hence a need in the art exists for a scanner driving mechanism capable of converting continuous rotary motion into oscillatory, wide angle scanning motion.